1. Field of the Invention
The present invention relates to a system for closing a conduit having a gripless inner surface, which is to be tested under pressure from an open inlet end.
Such a system is useful, for example, for periodic testing, by application of an overpressure, of the resistance of steam driers-superheaters in nuclear power stations. In fact, for carrying out an overpressure resistance test of such an apparatus, it is necessary to close the whole of the conduit which opens into this apparatus and in particular the conduit which in normal use brings the steam into the apparatus. Since it is important to check, at the same time, the pressure resistance of the connection between the drier-superheater and this conduit, the closure must be provided in the conduit beyond this connection, which corresponds therefore substantially to the open end of the conduit allowing the input of pressurized fluid during testing. In most cases, there is no grip on the inner surface of the conduit, which is therefore generally smooth coming straight from the braziery.
2. Description of the Prior Art
To close a conduit with a smooth inner surface, it is known to use a closure system formed essentially of an inflatable envelope, made for example from rubber, of a substantially cylindrical shape when it is inflated, and whose wall bears on the smooth inner surface of the conduit, under the effect of the pressure of a fluid with which the envelope is inflated. Sealing rings are generally formed on the outside of the walls of the envelope in contact with the inner surface of the conduit, so as to provide good sealing. Although such a system gives satisfaction in the case of a conduit of moderate diameter subjected to a pressure difference also moderate, it is unusable in the above described application, relating to pressure testing of a drier-superheater. In fact, in this case, the diameter of the conduit to be closed is generally of the order of 1.20 m and the testing pressure of the order of 20 bars. Now, in the case of a conduit of a diameter of 1.20 m, the maximum admitted pressure difference for an envelope of the above type is of the order of 0.3 bar. For higher pressure differences, adhesion of the envelope to the inner surface of the conduit is no longer ensured, and such an envelope cannot then be suitable for solving the problem raised.
For this, a sealing wall could be placed inside the conduit, an annular seal possibly inflatable being placed between the two. This would require the fitting of fixing means to the inner surface of the conduit, so as to maintain the wall in position before testing and immobilizing it so that it does not move under the action of the forces exerted on the wall during testing. Now, for questions of safety, it is not tolerable to take the risk of damaging the inner surface of the conduit, which must remain in its initial condition during and after testing. Moreover, a closure wall dimensioned so as to resist and not be deformed under the action of such stresses would be very heavy and so difficult to install inside the conduit, in a position difficult of access for remote from the inlet end.
The present invention aims at overcoming the above drawbacks by providing a closure system for a conduit having an inner gripless surface system which is capable of withstanding very high pressures in large diameter conduits, which requires the installation of no fixing means on the inner surface of the conduit and which is easy to position.